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Silicon Materials
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Silicon semiconductor devices are mostly fabricated on polished wafer or epitaxial wafer. Thus, the first step in device fabrication is the preparation of mirror polished, clean, and damage-free silicon surfaces in accordance with the specifications. As the design rule of device fabrication advances into the deep sub-micron region, the device processing and performance are more sensitive to the starting material’s characteristics. The requirements of the geometrical tolerance of the polished wafers as well as their bulk characteristics are becoming more stringent. The polished wafers are prepared through the complex sequence of shaping, polishing, and cleaning steps after a single crystal ingot is grown. Although the detailed shaping processes vary depending on the manufacturer. The processes described below are generic in nature. Newly introduced processing technologies will be discussed where appropriate. Figure 3.46 is a flow chart showing a generic wafer shaping process.
Terahertz generation and detection of 1550-nm-excited LT-GaAs photoconductive antennas
Published in Journal of Modern Optics, 2021
Zhi-Chen Bai, Xin Liu, Jing Ding, Hai-Lin Cui, Bo Su, Cun-Lin Zhang
The material of the photoconductive antenna determines the THz waveform. To improve the performance of the photoconductive antenna, our experiment uses molecular beam epitaxy equipment (MBE) to grow the epitaxial wafer [15]. The growth environment was maintained in an ultra-vacuum cavity (10–10 Pa). The deposition rate was kept below 1000 nm/h to ensure that only one atomic layer is grown at a time. The substrate is a 350-μm-thick SI-GaAs layer. First, the temperature is set to 580 °C to grow 80-nm-thick GaAs on SI-GaAs. Then, the temperature is set to 550 °C to grow 200-nm-thick AlAs on GaAs. Subsequently, the temperature is set to 200 °C to grow 2-μm-thick LT-GaAs on GaAs. Finally, the temperature is set to 615 °C and an annealing treatment is performed for 15 min to obtain the LT-GaAs epitaxial wafers [16–18]. A schematic diagram of the epitaxial wafer structure is shown in Figure 1. The 80-nm-thick GaAs layer is used as a buffer layer, and the 200-nm-thick AlAs layer is used as the sacrificial layer.
LT-GaAs Thin film antenna based on the asynchronous optical sampling system
Published in Journal of Modern Optics, 2022
Xin Liu, Boyan Zhang, Qingjun Li, Ping Ye, Bo Su, Jingsuo He, Cunlin Zhang
To fabricate the LT-GaAs thin film, this article employs the epitaxial wafer structure depicted in Figure 1. The molecular beam epitaxy (MBE) technology is used to grow the epitaxial wafer. The entire growing process takes place in an ultra-vacuum (10−10Pa) cavity. The material was deposited at a rate of less than 1000 nm/h, with only one atomic layer growing at a time. The MBE equipment can accurately control the deposition quality and deposition rate. The substrate is 2 in. of semi-insulating gallium arsenide (SI-GaAs). To improve crystal growth quality, we first grew an 80-nm-thick GaAs buffer layer at 580 °C on the substrate, then a 200-nm-thick AlAs sacrificial layer at 550 °C, and a 2-μm-thick GaAs layer at 200°C. The sample was then annealed for 15 min at 615°C. In the epitaxial wafer growth process, it is technically possible to directly grow AlAs on GaAs because the lattice constants of GaAs and AlAs are close. After the growth of the LT-GaAs crystal, a high-temperature annealing stage can improve the quality of the LT-GaAs crystal [16]. Among them, AlAs material can be corroded by HCl solution or HF solution. For the safety and simplicity of the experiment process, this experiment chooses an appropriate concentration of HCl solution to corrode the epitaxial wafer with a size of 2 × 2 mm. The HCl solution is made by mixing 38% concentrated hydrochloric acid and deionized water, and the volume ratio concentration value is calculated. The corrosion rate of the over-concentrated HCl solution and the AlAs sacrificial layer is faster, but it is not conducive to the complete acquisition of LT-GaAs film. Dilute concentrated hydrochloric acid with a concentration of 38% into hydrochloric acid solutions of different concentrations. After several tests, it was found that when the epitaxial wafer was etched with 13.57% HCl solution, the quality of the LT-GaAs film obtained was the best. Appropriate heating can also be selected to increase the corrosion rate even further. Figure 2 is a scanning electron microscope image of LT-GaAs thin film. The prepared single-layer LT-GaAs thin film is cleaned with deionized water and alcohol respectively and then transferred to a silicon wafer.